Tear resistant multilayer film

ABSTRACT

A tear resistant multilayer film including a stack of polymeric layers that includes first and second layer types. Layers of the first layer type includes a first polymer and the layers of the second layer type includes a second polymer. The first polymer is polyethylene terephthalate or a first ester block copolymer that includes polyethylene terephthalate blocks at a weight percent of the first ester block copolymer of at least 50 percent and further includes glycol-modified polyethylene terephthalate blocks. The second polymer is sebacic acid-substituted polyethylene terephthalate or a second ester block copolymer that includes sebacic acid-substituted polyethylene terephthalate blocks at a weight percent of the second ester block copolymer of at least 50 percent and further includes polyethylene terephthalate blocks or glycol-modified polyethylene terephthalate blocks. The tear resistant multilayer film includes a total of 8 to 300 layers of the first and second layer types.

BACKGROUND

Tear resistant multilayer films are known. For example, U.S. Pat. No.6,040,061 (Bland et al.) describes a tear resistant film having layersselected from a stiff polyester or copolyester, a ductile sebacic acidbased copolyester, and optionally, an intermediate material. Tearresistant multilayer films can be applied to glass to improve theshatter resistance of the glass.

SUMMARY

In some aspects of the present description, a tear resistant multilayerfilm including a stack of polymeric layers having first and second layertypes is provided. The polymeric layers of the first layer type includesa first polymer and the polymeric layers of the second layer typeincludes a second polymer. The polymeric layers are arranged such thatno two layers of the first layer type are immediately adjacent and suchthat no two layers of the second layer type are immediately adjacent.The first polymer is polyethylene terephthalate or a first ester blockcopolymer including polyethylene terephthalate blocks at a weightpercent of the first ester block copolymer of at least 50 percent, wherethe ester block copolymer further includes glycol-modified polyethyleneterephthalate blocks. The second polymer is sebacic acid-substitutedpolyethylene terephthalate or a second ester block copolymer includingsebacic acid-substituted polyethylene terephthalate blocks at a weightpercent of the second ester block copolymer of at least 50 percent,where the second ester block copolymer further includes polyethyleneterephthalate blocks, glycol-modified polyethylene terephthalate blocks,or a combination thereof. The tear resistant multilayer film includes atotal number of layers of the first and second layer types in a range of8 to 300. At least one of the following conditions is satisfied: (i) thefirst polymer is the first ester block copolymer and includesglycol-modified polyethylene terephthalate blocks at a weight percent ofthe first ester block copolymer of at least about 5 percent, and (ii)the second polymer is the second ester block copolymer and includespolyethylene terephthalate blocks, glycol-modified polyethyleneterephthalate blocks, or a combination thereof at a weight percent ofthe second ester block copolymer of at least about 5 percent.

In some aspects of the present description, a laminate is provided thatincludes a glass and the tear resistant multilayer film attached to theglass with an optically clear adhesive layer.

In some aspects of the present description, methods of making the tearresistant multilayer film are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a tear resistant multilayer film;

FIG. 2 is a cross-sectional view of a tear resistant multilayer film;

FIG. 3 is a schematic cross-sectional view of a laminate that includestwo tear resistant multilayer films; and

FIG. 4 is a schematic illustration of a process for making tearresistant multilayer films.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings that forms a part hereof and in which are shown by way ofillustration. The drawings are not necessarily to scale. It is to beunderstood that other embodiments are contemplated and may be madewithout departing from the scope or spirit of the present disclosure.

As used herein, layers, components, or elements may be described asbeing adjacent one another. Layers, components, or elements can beadjacent one another by being in direct contact, by being connectedthrough one or more other components, or by being held next to oneanother or attached to one another. Layers, components, or elements thatare in direct contact may be described as being immediately adjacent.

Tear resistant multilayer films that include a plurality of stiff layersand a plurality of ductile layers are known. However, such films aretypically made by laminating the various layers together with adhesivelayers and this adds unwanted costs to the films. Multilayer films canalternatively be made via a coextrusion process. However, whenconventional materials are coextruded to form a multilayer film having adesired thickness and tear resistance performance, the haze of themultilayer film can be too high for many applications. For example, insome cases it is desired to attach a tear resistant multilayer film to awindow for improved shatter resistance. It is typically desired for suchwindow films to have a low haze (e.g., less than 2 percent). Accordingto the present description, modified materials have been discovered thatallow multilayer films to be coextruded at sufficient thicknesses thatgood tear resistance performance is obtained without sacrificingclarity.

As described in U.S. Pat. No. 5,604,019 (Bland et al.) and U.S. Pat. No.6,040,061 (Bland et al.), for example, suitable stiff layers (which is afirst layer type) for multilayer films include polyethyleneterephthalate (PET) and suitable ductile layers (which is a second layertype) for multilayer films include sebacic acid-substituted polyethyleneterephthalate (SA-PET). Sebacic acid-substituted polyethyleneterephthalate refers to a polyethylene terephthalate with some of theterephthalic acid-derived moieties replaced with sebacic acid-derivedmoieties, and can be prepared by reacting terephthalic acid, sebacicacid and ethylene glycol. For example, SA-PET may be the reactionproduct of about 40 to about 80 mole equivalents terephthalic acid,about 40 to about 20 mole equivalents sebacic acid, and about 100 moleequivalents ethylene glycol. In some embodiments, SA-PET may be thereaction product of about 50 to about 70 mole equivalents terephthalicacid, about 50 to about 30 mole equivalents sebacic acid, and about 100mole equivalents ethylene glycol.

According to the present description, it has been found that improvedmultilayer film can be obtained by replacing SA-PET in the second layertypes with an ester block copolymer that includes SA-PET blocks and thatincludes PET blocks and/or glycol-modified polyethylene terephthalate(PETG) blocks. According to the present description, it has been foundthat improved multilayer film can be obtained by replacing PET in thefirst layer types with an ester block copolymer that includes PETGblocks. It has been found that a multilayer film using an ester blockcopolymer that includes SA-PET blocks as the second layer type and usingPET as a first layer type or that a multilayer film using SA-PET as thesecond layer type and using an ester block copolymer that includes PETGblocks as the first layer type provides improved optical and mechanicalproperties compared with multilayer films using SA-PET as the secondlayer type and PET as the first layer type. In some embodiments, boththe first and second layer types include ester block copolymers. Incontrast to conventional tear resistant multilayer films, the improvedmultilayer films of the present description can simultaneously be thick(e.g., 100 μm to 500 μm) and have a low haze (e.g., less than 2percent).

PET is commercially available from DuPont (Wilmington, Del.), forexample. PET can be formed as the reaction product of terephthalic acidand ethylene glycol. PETG can be formed from a similar reaction wheresome portion of the ethylene glycol is replaced with another componentsuch as cyclohexanedimethanol. In some embodiments, the PETG used in themultilayer films of the present description is the reaction product ofabout 100 mole equivalents terephthalic acid, about 70 to about 98 moleequivalents ethylene glycol and about 30 to about 2 mole equivalentscyclohexanedimethanol. In some embodiments, the PETG is the reactionproduct of about 100 mole equivalents terephthalic acid, about 90 toabout 98 mole equivalents ethylene glycol and about 10 to about 2 moleequivalents cyclohexanedimethanol. PETG is commercially available fromEastman Chemical (Kingsport, Tenn.) and SK Chemicals Co. Ltd. (Korea),for example.

Ester block copolymers are block copolymers that include blocks of afirst polyester and blocks of a second polyester different from thefirst polyester. Ester block copolymers may also include blocks of athird polyester (or fourth polyester or more) different from the firstand second polyester. Ester block copolymers can be made by atransesterification reaction where a first polyester is blended with asecond polyester under heat. Interactions between molecules of the firstpolyester and molecules of the second polyester result in exchanges ofportions of the molecules which produces new molecules having blocks ofthe first polyester and blocks of the second polyester. The variousweight fractions of the various blocks in the ester block copolymer canbe adjusted by changing the relative ratio of the polyesters added tothe transesterification reactor. As is discussed in greater detailelsewhere, transesterification reactions can take place through in-linereactive extrusion.

There are many polyesters that could be considered for forming blocks inan ester block copolymer that includes SA-PET blocks at greater thanabout 50 weight percent of the ester block copolymer. Such polyestersinclude, PET, PETG, polyethylene naphthalate (PEN), glycol-modified PEN(PENG), NEOSTAR Elastomer FN007 (a low Tg copolyester available fromEastman Chemical), a random copolymer of 90 mole percent PEN moietiesand 10 mole percent PET moieties (CoPEN9010), a blend of PET and PEN atan 80:20 ratio by weight, 50:50 by weight blends of PET and CoPEN9010,or PET and PENG, or PETG and PEN, or PETG and CoPEN9010, or PETG andPENG. Of these possibilities, it has been discovered that only PET andPETG are suitable for modifying SA-PET to form an ester block copolymerthat has desirable mechanical and processing properties and thatmaintains a low haze. It has been found that ester block copolymers thatincludes SA-PET at a weight percent of the ester block copolymer in arange from about 70 percent to about 95 percent and that includes PETblocks, PETG blocks, or a combination of PET blocks and PETG blocks in arange of about 5 percent to about 30 percent provides desirable haze andmechanical properties. A lower concentration of PET and/or PETG has beenfound to result in undesirable haze while a higher concentration hasbeen found to result in a stiffness that is too high for providing adesired degree of tear resistance.

Similarly, there are many polyesters that could be considered forforming blocks in an ester block copolymer that includes PET blocks atgreater than about 50 weight percent of the ester block copolymer. Ithas been found that ester block copolymers that includes PET blocks at aweight percent of the first ester block copolymer in a range from about60 percent to about 95 percent and that includes PETG blocks at a weightpercent of the ester block copolymer in a range from about 5 percent toabout 40 percent provides desirable haze and mechanical properties. Alower concentration of PETG has been found to result in undesirable hazewhile a higher concentration has been found to result in reduced straininduced crystallinity and/or reduced film processability (e.g., reducedheat set window) and this can result in polymer layers with poortoughness or poor stability.

In addition to providing improved optical and mechanical properties ofmultilayer films, the ester block copolymers of the present descriptionprovide improved rheological properties which can aid in the meltprocessing of the polymers. For example, a typical melt processingtemperature for PET is 280° C. At this temperature an ester blockcopolymer that includes 75 weight percent SA-PET blocks and 25 weightpercent of PET blocks or PETG blocks has a viscosity about twice that ofSA-PET. This can translate into up to about a 40° C. increase inprocessing temperature for the ester block copolymer and this can allowfor a more robust coextrusion that produces higher quality film (e.g.,film with fewer optical defects).

FIG. 1 is a cross-sectional view of multilayer film 100 which includes astack of polymeric layers 101 that includes layers of a first type 110and layers of a second type 112. The stack of polymeric layers 101includes a first outermost layer 114 and an opposite second outermostlayer 116. Layers of the first type 110 are formed from a first polymerand layers of the second type 112 are formed from a second polymerdifferent from the first polymer. The first polymer may be PET or afirst ester block copolymer that includes PET blocks at a weight percentof the first ester block copolymer of at least 50 percent and thatfurther includes PETG blocks. The second polymer may be SA-PET or asecond ester block copolymer that includes SA-PET blocks at a weightpercent of the second ester block copolymer of at least 50 percent andthat further includes PET blocks, PETG blocks, or both PET blocks andPETG blocks. In some embodiments, at least one of the first and secondpolymers are the first or second ester block copolymers, respectively.In some embodiments, one or both of the following conditions issatisfied: (i) the first polymer is the first ester block copolymer andincludes PETG blocks at a weight percent of the first ester blockcopolymer of at least about 5 percent, and (ii) the second polymer isthe second ester block copolymer and includes PET blocks, PETG blocks,or a combination of PET blocks and PETG blocks at a weight percent ofthe second ester block copolymer of at least about 5 percent.

In some embodiments, the second polymer is the second ester blockcopolymer and includes SA-PET at a weight percent of the second esterblock copolymer in a range from about 70 percent to about 95 percent orin a range from about 70 percent to about 90 percent. In someembodiments, the second polymer is the second ester block copolymer andincludes PET blocks, PETG blocks, or a combination of PET blocks andPETG blocks in a range of about 5 percent to about 30 percent or in arange of about 10 percent to about 30 percent.

In some embodiments, the first polymer is the first ester blockcopolymer and includes PET blocks at a weight percent of the first esterblock copolymer in a range from about 60 percent to about 95 percent orin a range of about 60 percent to about 90 percent. In some embodiments,the first polymer is the first ester block copolymer and includes PETGblocks at a weight percent of the first ester block copolymer in a rangefrom about 5 percent to about 40 percent or in a range from about 10percent to about 40 percent.

In some embodiments, the first polymer is the first ester blockcopolymer and the second polymer is the second ester block copolymer andthe first ester block copolymer includes PETG blocks at a weight percentof the first ester block copolymer in a range of about 5 percent toabout 40 percent and the second ester block copolymer includes PETblocks, PETG blocks, or a combination of PET blocks and PETG blocks at aweight percent of the second ester block copolymer in a range of about 5percent to about 30 percent.

An ester block copolymer that includes PET blocks at greater than 50weight percent of the ester block copolymer may be referred to asmodified PET. An ester block copolymer that includes SA-PET blocks atgreater than 50 weight percent of the ester block copolymer may bereferred to as modified SA-PET.

The layers of the first layer type may be stiff and the layers of thesecond layer type may be ductile. Stiff layers refers to layers having atensile modulus greater than 1.5 GPa or greater than 2 GPa as measuredaccording to ASTM D 882-12 at 23° C. Ductile layers refers to layersthat have a tensile modules less than 1.4 GPa or less than 1.0 GPa asmeasured according to ASTM D 882-12 at 23° C. and that has elongation atbreak of greater than 50 percent or greater than 100 percent accordingto ASTM D 882-12 at 23° C. The stiff layers may be PET or modified PETand the ductile layers may be SA-PET or modified SA-PET, where at leastsome of the stiff layers are modified PET or at least some of theductile layers are modified SA-PET. The stack of polymeric layers of thetear resistant multilayer films may include the ductile layers at aweight percent of the stack in a range from about 1 percent to about 20percent or in a range of about 5 percent to about 20 percent.Accordingly, the thickness of the ductile layers may be substantiallyless than that of the stiff layers. For example, the thickness of theductile layers may be only about 0.1 times the thickness of the stifflayers. Using a relatively low weight fraction of the ductile layersprovides significant improvements in the tear resistances of themultilayer films.

In some embodiments, the multilayer film 100 includes a stack ofpolymeric layers 101 that includes a total number of layers of the firstand second layer types 110 and 112 that is at least 6, or at least 7, orat least 8, or at least 9, or at least 10 and that is no more than 300,or no more than 200, or no more 100, or no more than 50, or no more than30, or no more than 20. For example, in some embodiments, the multilayerfilm 100 includes a stack of polymeric layers 101 that includes a totalnumber of layers of the first and second layer types 110 and 112 that isin the range of 8 to 300, or that is in the range of 9 to 30, or that isin the range of 10 to 20.

In the embodiment illustrated in FIG. 1, the stack of polymeric layers101 include alternating layers of the first and second layer types 110and 112. In alternate embodiments, additional layers of a third layertype, different from the first and second layer types, are included thatseparate layers of the first and second layer types 110 and 112. In suchembodiments, layers of the first and second layer types 110 and 112 maybe arranged in any order. For example, the first and second layer types110 and 113 may alternate from one type to the other or a random orpseudo-random distribution may be utilized. The ordering of thepolymeric layers may be selected such that no two layers of the firstlayer type 110 are immediately adjacent and such that no two layers ofthe second layer type 112 are immediately adjacent since two layers ofthe same layer type that were immediately adjacent could be described asa single thicker layer. In some embodiments, the stack of polymericlayers 101 consists essentially of alternating layers of the first andsecond layer types 110 and 112 with no layers of a third layer typeseparating layers of the first and second layer types 110 and 112. Inother embodiments, a third layer type may be included. For example, thethird layer type may be a tie layer that improves the interlayer bondingof dissimilar layers in the stack. Suitable tie layers are described inU.S. Pat. No. 6,040,061 (Bland et al.), for example.

The first and second outermost layers 114 and 116 can be either of thefirst or the second layer types 110 and 112. In the embodimentillustrated in FIG. 1, the first outermost layer 114 is a layer of thefirst layer type 110 and the second outermost layer 116 is a layer ofthe second layer type 112. In other embodiments, the first and secondoutermost layers 114 and 116 can be both be of the first layer type orof the second layer type. In still other embodiments, one or bothoutermost layers are of a layer type different from the first and secondlayer types.

In some embodiments, the stack of polymeric layers 101 is stretched sothat the polymeric layers are biaxially or uniaxially oriented. In someembodiments, the stack of polymeric layers 101 is stretched at a drawratio greater that about 1.5 or greater than about 2.0 and less thanabout 10.0 or less than about 6.0 in one or both in-plane directions(i.e., in the transverse direction (TD) and/or in the machine direction(MD)). Orienting the polymeric layers can improve the mechanicalproperties (e.g., tensile modulus) of the layers and can result in amultilayer film having a higher tear resistance.

Tear resistance can be determined using a Graves tear test as describedin ASTM D1004-13 “Standard Test Method for Tear Resistance (Graves Tear)of Plastic Film and Sheeting”. The Graves tear test determines a tearresistance (maximum force) and an elongation at break. In someembodiments, a multilayer film according to the present description hasa Graves tear resistance of at least about 25 N, or at least about 50 N,or at least about 100 N and may be up to about 300 N or up to about 500N, in each of a first direction and a second direction different fromthe first direction and has a Graves elongation at break of at leastabout 20 percent, or at least about 30 percent, or at least about 40percent, and may be up to about 100 percent, or up to about 200 percent,in each of the first and second directions. For example, in someembodiments, a multilayer film according to the present description hasa Graves tear resistance in a range of about 25 N to about 500 N in eachof a first direction and a second direction different from the firstdirection and has a Graves elongation at break in a range of about 20percent to about 200 percent in each of the first and second directions.The first and second directions may refer to principle in-plane axes ofthe film which may be the TD direction and the MD direction,respectively. The first and second directions may be orthogonal orsubstantially orthogonal in-plane directions.

The Graves tear test allows an applied force as a function of thepercent elongation of the test sample to be determined Graves Arearefers to the area under the force versus percent elongation curve andmay be expressed in units of a force times a percent. The Graves Area isa useful measure of the toughness of a tear resistant film. In someembodiments, the multilayer tear resistant film has a Graves Area of atleast 1 kN x %, or at least 2 kN x %, or at least 3 kN x %, and may beup to about 10 kN x %, or up to about 20 kN x %, in each of a first anda second direction which may be the TD direction and the MD direction,respectively. For example, in some embodiments, the multilayer tearresistant film has a Graves Area in the range of about 1 kN x % to about20 kN x % in each of the MD and TD directions.

Tear resistance can also be measured using a puncture-propagation tearresistance test. As used herein, PPT tear resistance refers to thepuncture-propagation tear resistance determined as described in ASTMD2582-09 except that a carriage weight of 698.5 grams and a drop heightof 17.0 cm is used in the test, unless indicated otherwise. In someembodiments, the multilayer tear resistant film has a PPT tearresistance of at least 2 kg or at least 2.5 kg in each of a first and asecond direction which may be the TD direction and the MD direction,respectively. In some embodiments, the multilayer tear resistant filmhas a PPT tear resistance in the range of about 2 kg to about 10 kg ineach of the MD and TD directions.

FIG. 2 is a cross-sectional view of multilayer film 200 which includes astack of polymeric layers 201 that has a first outermost layer 214 and asecond outermost layer 216 opposite the first outermost layer 214. Thestack of polymeric layers 201 may correspond to the stack of polymericlayers 101 of FIG. 1. A primer layer 220 is disposed on the firstoutermost layer 214 and a hard coat layer 225 is disposed on the primerlayer 220. An optically clear adhesive layer 230 is disposed on thesecond outermost layer 216.

Suitable materials for primer layer 220 include 3M Primer 94, forexample, which is available from 3M Company (St. Paul, Minn.). Othersuitable primers include chemistries of ionomer, polyvinylidene chloride(PVDC), and/or amine based moieties. In alternative embodiments, asurface treatment, such a flame or corona discharge treatment is appliedto first outermost layer 214 and no primer layer is included betweenfirst outermost layer 214 and hard coat layer 225. Suitable materialsfor hard coat layer 225 includes radiation (e.g., ultraviolet) curablematerials such as an acrylate or methacrylate. The acrylate ormethacrylate may include nanoparticles to increase the hardness of thehard coat. Suitable hard coats include those described in U.S. Pat. App.Pub. No. 2013/0302594 (Sugiyama et al.), for example. Suitable adhesivelayers useful for optically clear adhesive layer 230 include 3MOptically Clear Adhesives 8171 and 8172, for example, both availablefrom 3M Company (St. Paul, Minn.). Other suitable adhesives may bederived from chemistries such as acrylic, polyester, polyurethane,polyolefin, and/or silicone. In some embodiments, the second outermostlayer 216 is surface treated prior to applying optically clear adhesivelayer 230.

Haze can be defined as the percent of transmitted light that isscattered so that its direction deviates more than 2.5 degrees from thedirection of the incident beam as specified in ASTM D1003-13 “StandardTest Method for Haze and Luminous Transmittance of TransparentPlastics”. Haze can be determined using a HAZE-GARD PLUS meter availablefrom BYK-Gardner Inc. (Silver Springs, Md.) which is said to comply withthe ASTM D1003-13 standard. In some embodiments, the multilayer film 200is substantially transparent. For example, the multilayer film 200 mayhave a total luminous transmittance of at least 85 percent or at least90 percent according to the ASTM D1003-13 standard. In some embodiments,the haze of multilayer film 200 or the haze of the stack of polymericlayers 201 may be less than about 2.0 percent, less than about 1.75percent, less than about 1.5 percent, less than about 1.25 percent, orless than about 1.0 percent and may be as low as about 0.5 percent orabout 0.2 percent. For example, in some embodiments, the haze ofmultilayer film 200 or the haze of the stack of polymeric layers 201 maybe in a range of about 0.2 percent to about 2.0 percent.

In some embodiments, the thickness of multilayer film 200 or thethickness of the stack of polymeric layers 201 may be greater than about50 microns, greater than about 100 microns, or greater than about 150microns and may be less than about 600 microns or less than about 500microns.

In some embodiments, multilayer film 200 is a tear resistant film thatis suitable for use as a window film. Such a window film can prevent awindow from shattering. In some embodiments, a window film is attachedto one major surface of a glass and in some embodiments, window filmsare attached to both major surfaces of a glass.

FIG. 3 is a schematic cross-sectional view of laminate 305 that includesglass 340 having first major surface 342 and opposite second majorsurface 344. Laminate 305 includes first and second multilayer films 300a and 300 b. Each of the first and second multilayer films 300 a and 300b may correspond to multilayer film 200 and may include a polymericstack and an optically clear adhesive layer. First multilayer film 300 ais attached to glass 340 with the optically clear adhesive layer of thefirst multilayer film 300 a disposed on the first major surface 342.Second multilayer film 300 b is attached to glass 340 with the opticallyclear adhesive layer of the second multilayer film 300 b disposed on thesecond major surface 344.

FIG. 4 is a schematic illustration of a process for making a multilayerfilm according to the present description that includes in-line reactiveextrusion to produce an ester block copolymer. A first polyester 447 anda second polyester 449 are fed into extruder 450 which melts and mixesthe polyesters. Extruder 450 feeds the resulting melt stream into necktube 454 which feeds a first polymer 456 in its molten state intofeedblock 460. The melt stream through extruder 450 and neck tube 454has a high temperature so that transesterification reactions take placebetween first and second polyesters 447 and 449 resulting in a firstpolymer 456 which is an ester block copolymer. In some embodiments, themelt stream has a temperature in the range of 200° C. to 350° C. forabout 1 minute to about 5 minutes while the melt stream is in extruder450 and for about 10 minutes to about 20 minutes while the melt streamis in neck tube 454. The extruder 450 may be a single screw extruder ora twin screw extruder and may include a gear pump. The extruder 450 mayprovide a high shear and may operate at about 100 to about 500revolutions per minute (RPM). The extruder 450 may produce a pressure inthe range of about 3 MPa to about 15 MPa in neck tube 454. In someembodiments, additional polyesters may be fed into extruder 450 to forman ester block copolymer having more than two types of blocks. Forexample, a modified SA-PET ester block copolymer can be made by feedingSA-PET, PET and PETG into an in-line reactive extruder.

Since first polymer 456 is formed through a transesterification reactionthat takes place as it passes through extruder 450 and neck tube 454,the process for forming first polymer 456 may be referred to as in-linereactive extrusion. A second polymer 458 is fed into feedblock 460 inits molten form. Second polymer 458 may also be an ester block copolymerthat is formed through in-line reactive extrusion or may be a polymerthat is not an ester block copolymer or may be an ester block copolymerformed in a different process (e.g., a batch transesterificationprocess). In alternate embodiments, the second polymer 458 is an esterblock copolymer formed through in-line reactive extrusion and the firstpolymer 456 is not an ester block copolymer or is an ester blockcopolymer formed through a different process.

Feedblock 460 provides multilayer flows to coextrusion die 470 whichproduces a multilayer melt 475 that is cooled at casting station 480which produces un-stretched multilayer film 485. Suitable coextrusiondies are described in U.S. Pat. No. 6,767,492 (Norquist et al.), forexample. Casting station 480 may include a chill roll to quenchmultilayer melt 475. Un-stretched multilayer film 485 is stretched onstretcher 490, which may be a length orienter, or a tenter framestretcher, or a combination of a length orienter and a tenter framestretcher in sequence, and may biaxially or uniaxially stretch theun-stretched multilayer film 485 to produce stretched multilayer film495. Stretcher 490 may stretch the multilayer film in two directionsequentially (e.g., stretch in the machine direction and then stretch inthe transverse direction) or may simultaneously stretch in two in-planedirections. Additional processing steps may be included to add a primerand a hardcoat layer to one major surface of multilayer film 495 and/orto add an adhesive layer to the opposite major surface of multilayerfilm 495.

EXAMPLES Materials

Modified PET refers to an ester block copolymer that includes PET blocksat greater than 50 weight percent of the ester block copolymer. ModifiedSA-PET refers to an ester block copolymer that includes SA-PET blocks atgreater than 50 weight percent of the ester block copolymer.

SA-PET pellets were obtained from Dow Chemical (Midland, Mich.).

Nanya 1N502 PET pellets were obtained from Nanya Technology Corporation(Taiwan).

Nanya 1N404 PET pellets were obtained from Nanya Technology Corporation(Taiwan).

PETG pellets were obtained from Eastman Chemical (Kingsport, Tenn.)under the tradename PETg 6763.

Test Methods

Haze of film samples was determined using a HAZE-GARD PLUS meteravailable from BYK-Gardner Inc. (Silver Springs, Md.) according to ASTMD1003-13.

Graves tear resistance was determined according to ASTM D1004-13 inwhich a sample is cut with a die specified in the test standard and aforce is applied to the sample using a constantrate-of-crosshead-movement type testing machine to tear the sample. Anapplied force as a function of the percent elongation of the sample canbe determined from the test. The Graves Area in each of the MD and TDdirections was determined as the area under the force versus percentelongation curve.

Puncture-Propagation Tear (PPT) resistance was determined as describedin ASTM D2582-09 except that a carriage weight of 698.5 grams and a dropheight of 17.0 cm was used.

Modified SA-PET Film

Modified SA-PET cast webs were prepared by reacting the polymers of PET(Nanya 1N502 PET) and SA-PET in the various ratios listed in Table 1.The reaction took place in an in-line reactive extrusion process. Thepolymers experienced distributions of temperatures, pressures andreaction times as the polymers flowed through the in-line reactor. Thereaction conditions were selected such that the distribution oftemperatures was in the range of 200-300° C., the distribution ofpressures was in the range of 500 psi (3.4 MPa)-2000 psi (13.8 MPa), anddistribution of reaction times was in the range of 3 min to 30 min. Theconditions were chosen so that the blocky structure would be presentwithout completely randomizing the polyester structures. The reactionwas done using a twin screw extruder with processing variablescontrolled to achieve the above reaction conditions. The molten melt wasthen cast on a chilled roll held at a temperature in the range of about20° C. to about 50° C. to obtain a cast web.

The haze of cast webs of various modified SA-PET block copolymers and ofSA-PET were measured. The cast webs had a thickness of about 30 mils(0.76 mm) The haze of the SA-PET cast web was about 60.3 percent. Thehaze of the modified SA-PET cast webs after 7 days aging at RT and 50%humidity are reported in Table 1.

TABLE 1 Wt. % SA-PET Wt. % PET Wt. % PETG Blocks Blocks Blocks Haze (%)95 5 0 69.4 95 0 5 53.0 90 10 0 24.7 90 0 10 12.7 85 15 0 15.8 85 0 155.5 75 25 0 4.4 75 0 25 4.3

PET/PETG Ester Block Copolymer Film

PET/PETG ester block copolymer cast webs were prepared by reacting thepolymers of PET (Nanya 1N502 PET) and PETG in the various ratios listedin Table 2. The reaction took place in an in-line reactive extrusionprocess. The polymers experienced distributions of temperatures,pressures and reaction times as the polymers flowed through the in-linereactor. The reaction conditions were selected such that thedistribution of temperatures was in the range of 200-300° C., thedistribution of pressures was in the range of 500 psi (3.4 MPa)-2000 psi(13.8 MPa), and distribution of reaction times was in the range of 3 minto 30 min. The conditions were chosen so that the blocky structure wouldbe present without completely randomizing the polyester structures. Thereaction was done using a twin screw extruder with processing variablescontrolled to achieve the above reaction conditions. The molten melt wasthen cast on a chilled roll held at a temperature in the range of about20° C. to about 50° C. to obtain a cast web.

The haze of cast webs of various PET/PETG ester block copolymer filmsand of PET and PETG films were measured. The cast webs had a thicknessof about 50 mils (1.3 mm) The measured values of haze of the cast websafter 7 days aging at RT and 50% humidity are reported in Table 2.

TABLE 2 Wt. % PET Wt. % PETG Blocks Blocks Haze (%) 100 0 9.7 80 20 4.160 40 3.2 50 50 3.1 40 60 2.6 20 80 1.4 0 100 1.3

The various cast webs were biaxially stretched at a draw ratio of about3.5×3.5 to produce 4 mil (102 μm) films. The haze of the films after 7days aging at RT and 50% humidity were measured and are reported inTable 3.

TABLE 3 Wt. % PET Wt. % PETG Blocks Blocks Haze (%) 100 0 2.90 80 200.87 60 40 0.66 50 50 0.73 40 60 0.50 20 80 0.33 0 100 0.33

Comparative Example C-1

PET (Nanya 1N404 PET) resin was fed through a single screw extruder at afeeding rate of about 1900 kg/hr and SA-PET resin was fed through a twinscrew extruder at a feeding rate of about 90 kg/hr. The melt temperaturefor PET was about 546° F. (286° C.) and the melt temperature for SA-PETwas about 495° F. (257° C.). The melt streams were guided into a13-layer feedblock to form alternating layers of PET and SA-PET. Themelt was then spread in a film die and cast on a chilled roll to formcast web. The cast web was then sequentially stretched in the MDdirection and the TD direction at draw ratios of 3.2 and 3.3,respectively. The cast line speed was adjusted such that the finishedfilm thickness was about 8 mils (203 μm).

Example 1

PET (Nanya 1N404 PET) and PETG at a weight ratio of 80 to 20 was fedthrough a single screw extruder at a total feeding rate of about 1900kg/hr under the processing conditions described under “PET/PETG EsterBlock Copolymer Film” to produce a modified PET melt stream. SA-PETresin was fed through a twin screw extruder at a feeding rate of about90 kg/hr to produce an SA-PET melt stream. The melt temperature formodified PET was about 546° F. (286° C.) and the melt temperature forSA-PET was about 495° F. (257° C.). The melt streams were guided into a13-layer feedblock to form alternating layers of modified PET andSA-PET. The melt was then spread in a film die and cast on a chilledroll to form cast web. The cast web was then sequentially stretched inthe MD direction and the TD direction at draw ratios of 3.2 and 3.3,respectively. The cast line speed was adjusted such that the finishedfilm thickness was about 8 mils (203 μm).

Example 2

PET (Nanya PET 1N404) and PETG at a weight ratio of 80 to 20 was fedthrough a single screw extruder at a total feeding rate of about 1900kg/hr under the processing conditions described under “PET/PETG EsterBlock Copolymer Film” to produce a modified PET melt stream. SA-PET andPETG at a weight ratio of 80 to 20 was fed through a twin screw extruderat a total feeding rate of about 90 kg/hr under the processingconditions described under “Modified SA-PET Film” to produce a modifiedSA-PET melt stream. The melt temperature for the modified PET was about546° F. (286° C.) and the melt temperature for the modified SA-PET wasabout 495° F. (257° C.). The melt streams were guided into a 13-layerfeedblock to form alternating layers of modified PET and modifiedSA-PET. The melt was then spread in a film die and cast on a chilledroll to form cast web. The cast web was then sequentially stretched inthe MD direction and the TD direction at draw ratios of 3.2 and 3.3,respectively. The cast line speed was adjusted such that the finishedfilm thickness was about 8 mils (203 μm).

The haze of the finished films of Comparative Example C-1 and ofExamples 1-2 was monitored using a HAZE-GARD PLUS haze meter for aperiod of time of 8 days to identify the haze difference among thedifferent material compositions. The haze was observed to rise over afew days and then to stabilize. The resulting stabilized haze values arereported in Table 4.

TABLE 4 Example Haze (%) C-1 2.2 1 1.6 2 0.9

Graves tear resistance and PPT tear resistance of the finished filmswere measured in the MD and TD directions. The Graves maximum force andGraves maximum elongation at break are reported in Table 5 and theGraves Area and PPT tear resistance are reported in Table 6.

The results show that haze can be significantly lowered compared toComparative Example C-1 while adequate tear resistance is maintained.

TABLE 5 Graves Graves Graves Graves Force, Force, Percent PercentExample MD (N) TD (N) Elongation, MD Elongation, TD C-1 169.1 171.3 46.349.4 1 157.5 158 45.3 50.2 2 158.4 164.2 33.3 32.5

TABLE 6 Graves Area, MD Graves Area, TD PPT, MD PPT, TD Example (N × %)(N × %) (grams) (grams) C-1 4619 4744 3440 4690 1 4143 5029 3063 4393 22830 2875 2943 4393

Additional examples can be prepared by feeding the modified SA-PET meltstream of Example 2 and a conventional PET melt stream into a 13-layerfeedblock, for example, to form alternating layers of PET and modifiedSA-PET. The resulting 13-layer melt can then be cast and stretched as inExample 2. Further examples can be prepared by modifying the proportionsof PET and PETG used to make a modified PET melt stream and/or theproportions of SA-PET and PETG used to make a modified SA-PET meltstream as described under “PET/PETG Ester Block Copolymer Film” and“Modified SA-PET Film”, respectively.

The following is a list of exemplary embodiments of the presentdescription.

-   -   Embodiment 1 is a tear resistant multilayer film comprising:        -   a stack of polymeric layers comprising first and second            layer types, the polymeric layers of the first layer type            comprising a first polymer and the polymeric layers of the            second layer type comprising a second polymer, the polymeric            layers arranged such that no two layers of the first layer            type are immediately adjacent and such that no two layers of            the second layer type are immediately adjacent,        -   wherein the first polymer is polyethylene terephthalate or a            first ester block copolymer comprising polyethylene            terephthalate blocks at a weight percent of the first ester            block copolymer of at least 50 percent, the ester block            copolymer further comprising glycol-modified polyethylene            terephthalate blocks;        -   wherein the second polymer is sebacic acid-substituted            polyethylene terephthalate or a second ester block copolymer            comprising sebacic acid-substituted polyethylene            terephthalate blocks at a weight percent of the second ester            block copolymer of at least 50 percent, the second ester            block copolymer further comprising polyethylene            terephthalate blocks, glycol-modified polyethylene            terephthalate blocks, or a combination thereof;        -   wherein the tear resistant multilayer film includes a total            number of layers of the first and second layer types in a            range of 8 to 300; and        -   wherein at least one following conditions is satisfied:            -   (i) the first polymer is the first ester block copolymer                and comprises glycol-modified polyethylene terephthalate                blocks at a weight percent of the first ester block                copolymer of at least about 5 percent, and            -   (ii) the second polymer is the second ester block                copolymer and comprises polyethylene terephthalate                blocks, glycol-modified polyethylene terephthalate                blocks, or a combination thereof at a weight percent of                the second ester block copolymer of at least about 5                percent.    -   Embodiment 2 is the tear resistant multilayer film of embodiment        1, wherein the second polymer is the second ester block        copolymer and comprises sebacic acid-substituted polyethylene        terephthalate blocks at a weight percent of the second ester        block copolymer in a range from about 70 percent to about 90        percent.    -   Embodiment 3 is the tear resistant multilayer film of embodiment        1, wherein the second polymer is the second ester block        copolymer and comprises polyethylene terephthalate blocks,        glycol-modified polyethylene terephthalate blocks, or a        combination thereof at a weight percent of the second ester        block copolymer in a range from about 5 percent to about 30        percent.    -   Embodiment 4 is the tear resistant multilayer film of embodiment        1, wherein the first polymer is the first ester block copolymer        and comprises polyethylene terephthalate blocks at a weight        percent of the first ester block copolymer in a range from about        60 percent to about 95 percent.    -   Embodiment 5 is the tear resistant multilayer film of embodiment        1, wherein the first polymer is the first ester block copolymer        and comprises glycol-modified polyethylene terephthalate blocks        at a weight percent of the first ester block copolymer in a        range from about 5 percent to about 40 percent.    -   Embodiment 6 is the tear resistant multilayer film of embodiment        1, wherein the first polymer is the first ester block copolymer        and the second polymer is the second ester block copolymer and        wherein the first ester block copolymer comprises        glycol-modified polyethylene terephthalate blocks at a weight        percent of the first ester block copolymer of at least about 5        percent and the second ester block copolymer comprises        polyethylene terephthalate blocks, glycol-modified polyethylene        terephthalate blocks, or a combination thereof at a weight        percent of the second ester block copolymer of at least about 5        percent.    -   Embodiment 7 is the tear resistant multilayer film of embodiment        6, wherein the first ester block copolymer comprises        glycol-modified polyethylene terephthalate blocks at a weight        percent of the first ester block copolymer in a range of about 5        percent to about 40 percent and the second ester block copolymer        comprises polyethylene terephthalate blocks, glycol-modified        polyethylene terephthalate blocks, or a combination thereof at a        weight percent of the second ester block copolymer in a range of        about 5 percent to about 30 percent.    -   Embodiment 8 is the tear resistant multilayer film of embodiment        1, wherein the sebacic acid-substituted polyethylene        terephthalate or the sebacic acid-substituted polyethylene        terephthalate blocks comprises the reaction product of about 50        to about 70 mole equivalents terephthalic acid, about 50 to        about 30 mole equivalents sebacic acid, and about 100 mole        equivalents ethylene glycol.    -   Embodiment 9 is the tear resistant multilayer film of embodiment        1, wherein at least one of the first and second polymers        comprise glycol-modified polyethylene terephthalate blocks that        comprise the reaction product of about 100 mole equivalents        terephthalic acid, about 70 to about 98 mole equivalents        ethylene glycol and about 30 to about 2 mole equivalents        cyclohexanedimethanol.    -   Embodiment 10 is the tear resistant multilayer film of        embodiment 1, wherein the total number of layers of the first        and second layer types is in a range of 9 to 30.    -   Embodiment 11 is the tear resistant multilayer film of        embodiment 1, wherein the tear resistant multilayer film is        substantially transparent and has a haze less than about 2        percent.    -   Embodiment 12 is the tear resistant multilayer film of        embodiment 1, wherein the tear resistant multilayer film has a        Graves Area of at least 1000 N x % in each of a first direction        and a second direction different from the first direction.    -   Embodiment 13 is the tear resistant multilayer film of        embodiment 1, wherein the polymeric layers are biaxially        oriented.    -   Embodiment 14 is the tear resistant multilayer film of        embodiment 1, wherein the first and second layer types alternate        in the stack.    -   Embodiment 15 is the tear resistant multilayer film of        embodiment 1 further comprising a primer layer disposed on a        first outermost layer of the stack of polymeric layers and a        hard coat layer disposed on the primer layer.    -   Embodiment 16 is the tear resistant multilayer film of        embodiment 15 further comprising an optically clear adhesive        layer disposed on a second outermost layer of the stack of        polymeric layers opposite the first outermost layer of the stack        of polymeric layers.    -   Embodiment 17 is a laminate comprising:        -   a glass having a first major surface and an opposing second            major surface; and        -   a first tear resistant multilayer film according to            embodiment 16 attached to the glass, the optically clear            adhesive layer of the first tear resistant multilayer film            disposed on the first major surface of the glass.    -   Embodiment 18 is the laminate of embodiment 17 further        comprising a second tear resistant multilayer film according to        embodiment 16 attached to the glass opposite the first tear        resistant multilayer film, the optically clear adhesive layer of        the second tear resistant multilayer film disposed on the second        major surface of the glass.    -   Embodiment 19 is a method of making the tear resistant        multilayer film of embodiment 1 comprising the step of        coextruding a plurality of layers of the first and second        polymers in their molten states.    -   Embodiment 20 is the method of embodiment 19, wherein at least        one of the first and second polymers is formed by        transesterification of two or more polyesters through in-line        reactive extrusion at temperature range from 200° C. to 350° C.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations can besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present disclosure. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisdisclosure be limited only by the claims and the equivalents thereof

What is claimed is:
 1. A tear resistant multilayer film comprising: astack of polymeric layers comprising first and second layer types, thepolymeric layers of the first layer type comprising a first polymer andthe polymeric layers of the second layer type comprising a secondpolymer, the polymeric layers arranged such that no two layers of thefirst layer type are immediately adjacent and such that no two layers ofthe second layer type are immediately adjacent, wherein the firstpolymer is polyethylene terephthalate or a first ester block copolymercomprising polyethylene terephthalate blocks at a weight percent of thefirst ester block copolymer of at least 50 percent, the ester blockcopolymer further comprising glycol-modified polyethylene terephthalateblocks; wherein the second polymer is sebacic acid-substitutedpolyethylene terephthalate or a second ester block copolymer comprisingsebacic acid-substituted polyethylene terephthalate blocks at a weightpercent of the second ester block copolymer of at least 50 percent, thesecond ester block copolymer further comprising polyethyleneterephthalate blocks, glycol-modified polyethylene terephthalate blocks,or a combination thereof; wherein the tear resistant multilayer filmincludes a total number of layers of the first and second layer types ina range of 8 to 300; and wherein at least one following conditions issatisfied: (i) the first polymer is the first ester block copolymer andcomprises glycol-modified polyethylene terephthalate blocks at a weightpercent of the first ester block copolymer of at least about 5 percent,and (ii) the second polymer is the second ester block copolymer andcomprises polyethylene terephthalate blocks, glycol-modifiedpolyethylene terephthalate blocks, or a combination thereof at a weightpercent of the second ester block copolymer of at least about 5 percent.2. The tear resistant multilayer film of claim 1, wherein the secondpolymer is the second ester block copolymer and comprises sebacicacid-substituted polyethylene terephthalate blocks at a weight percentof the second ester block copolymer in a range from about 70 percent toabout 90 percent.
 3. The tear resistant multilayer film of claim 1,wherein the second polymer is the second ester block copolymer andcomprises polyethylene terephthalate blocks, glycol-modifiedpolyethylene terephthalate blocks, or a combination thereof at a weightpercent of the second ester block copolymer in a range from about 5percent to about 30 percent.
 4. The tear resistant multilayer film ofclaim 1, wherein the first polymer is the first ester block copolymerand comprises polyethylene terephthalate blocks at a weight percent ofthe first ester block copolymer in a range from about 60 percent toabout 95 percent.
 5. The tear resistant multilayer film of claim 1,wherein the first polymer is the first ester block copolymer andcomprises glycol-modified polyethylene terephthalate blocks at a weightpercent of the first ester block copolymer in a range from about 5percent to about 40 percent.
 6. The tear resistant multilayer film ofclaim 1, wherein the first polymer is the first ester block copolymerand the second polymer is the second ester block copolymer and whereinthe first ester block copolymer comprises glycol-modified polyethyleneterephthalate blocks at a weight percent of the first ester blockcopolymer of at least about 5 percent and the second ester blockcopolymer comprises polyethylene terephthalate blocks, glycol-modifiedpolyethylene terephthalate blocks, or a combination thereof at a weightpercent of the second ester block copolymer of at least about 5 percent.7. The tear resistant multilayer film of claim 6, wherein the firstester block copolymer comprises glycol-modified polyethyleneterephthalate blocks at a weight percent of the first ester blockcopolymer in a range of about 5 percent to about 40 percent and thesecond ester block copolymer comprises polyethylene terephthalateblocks, glycol-modified polyethylene terephthalate blocks, or acombination thereof at a weight percent of the second ester blockcopolymer in a range of about 5 percent to about 30 percent.
 8. The tearresistant multilayer film of claim 1, wherein the sebacicacid-substituted polyethylene terephthalate or the sebacicacid-substituted polyethylene terephthalate blocks comprises thereaction product of about 50 to about 70 mole equivalents terephthalicacid, about 50 to about 30 mole equivalents sebacic acid, and about 100mole equivalents ethylene glycol.
 9. The tear resistant multilayer filmof claim 1, wherein at least one of the first and second polymerscomprise glycol-modified polyethylene terephthalate blocks that comprisethe reaction product of about 100 mole equivalents terephthalic acid,about 70 to about 98 mole equivalents ethylene glycol and about 30 toabout 2 mole equivalents cyclohexanedimethanol.
 10. The tear resistantmultilayer film of claim 1, wherein the total number of layers of thefirst and second layer types is in a range of 9 to
 30. 11. The tearresistant multilayer film of claim 1, wherein the tear resistantmultilayer film is substantially transparent and has a haze less thanabout 2 percent.
 12. The tear resistant multilayer film of claim 1,wherein the tear resistant multilayer film has a Graves Area of at least1000 N x % in each of a first direction and a second direction differentfrom the first direction.
 13. The tear resistant multilayer film ofclaim 1, wherein the polymeric layers are biaxially oriented.
 14. Thetear resistant multilayer film of claim 1, wherein the first and secondlayer types alternate in the stack.
 15. The tear resistant multilayerfilm of claim 1 further comprising a primer layer disposed on a firstoutermost layer of the stack of polymeric layers and a hard coat layerdisposed on the primer layer.
 16. The tear resistant multilayer film ofclaim 15 further comprising an optically clear adhesive layer disposedon a second outermost layer of the stack of polymeric layers oppositethe first outermost layer of the stack of polymeric layers.
 17. Alaminate comprising: a glass having a first major surface and anopposing second major surface; and a first tear resistant multilayerfilm according to claim 16 attached to the glass, the optically clearadhesive layer of the first tear resistant multilayer film disposed onthe first major surface of the glass.
 18. The laminate of claim 17further comprising a second tear resistant multilayer film according toclaim 16 attached to the glass opposite the first tear resistantmultilayer film, the optically clear adhesive layer of the second tearresistant multilayer film disposed on the second major surface of theglass.
 19. A method of making the tear resistant multilayer film ofclaim 1 comprising the step of coextruding a plurality of layers of thefirst and second polymers in their molten states.
 20. The method ofclaim 19, wherein at least one of the first and second polymers isformed by transesterification of two or more polyesters through in-linereactive extrusion at temperature range from 200° C. to 350° C.